Lithography is often used in the fabrication of microelectronic devices. As is well known to those having skill in the art, during lithography, a geometrical pattern in a mask or reticle is transferred to a thin layer of photosensitive material, referred to as a photoresist, on the surface of a wafer. The pattern may be used to define various regions on the wafer, such as ion implantation regions, contact holes, metal lines, bonding pads and the like.
In lithography, the patterned photoresist layer is generally not a permanent part of the microelectronic device. Rather, the photoresist pattern is generally transferred to an underlying layer using a selective etch process. The photoresist is then generally removed. The etched layer may or may not become a permanent part of the semiconductor device.
A conventional wafer patterning method will now be described with reference to FIGS. 1-3. FIG. 1 is a plan view of a semiconductor wafer after it has been patterned using conventional lithography. As shown in FIG. 1, because the size of the semiconductor wafer is larger than that of an integrated circuit chip, a plurality of patterns having the same shape or different shapes can be formed on wafer 1. Accordingly, the exposure process is generally carried out by repeatedly exposing a patterned reticle 2 while the wafer 1 moves two-dimensionally in the exposure apparatus, to thereby repeatedly form the same pattern on the wafer. As shown in FIG. 1, four chip patterns are formed in one reticle 2. However, it will be understood by those having skill in the art that larger or smaller numbers of patterns may be formed.
Since the shape of the wafer 1 is generally circular or oval, but the patterns 3 which are formed on the chip are generally rectangular, an active region 5 of the wafer 1 is limited to the central portion of the wafer. The peripheral region 4 of the wafer 1, between the active region 5 and the wafer edge, generally does not contain active semiconductor devices and is generally cut from the wafer during the chip scribing process.
FIG. 2 is a cross-sectional view taken along line A--A of FIG. 1, and which illustrates a patterning process according to a conventional lithography process. An etch stop 11 and a layer 12 are sequentially formed on a semiconductor substrate 10. A patterned photoresist layer 14 is formed on active region 5 and a blanket photoresist region 13 is formed on peripheral region 4. Regions 13 and 14 are generally formed by blanket depositing a photoresist layer on wafer 1 and repeatedly stepping a patterned reticle over the active region. As is well known to those having skill in the art, the reticle may include a predetermined pattern which is formed in a metal film and which is aligned to the wafer. Ultraviolet rays or other radiation is irradiated through the reticle to expose the photoresist layer. The exposure operation is repeatedly performed while the wafer and reticle are stepped in two directions to thereby expose the active region 5. The photoresist is then developed to remove the patterned photoresist, thus forming the structure of FIG. 2. As is well known to those having skill in the art, during the developing process, the photoresist layer 13 in the peripheral region and the unexposed portions of the photoresist layer 14 in the active region of the wafer are not removed, but remain on the wafer.
FIG. 3 illustrates a cross-sectional view of the wafer of FIG. 2 after etching. The photoresist layers 13 and 14 serve as an etch mask so that the pattern of the photoresist layer 14 is transferred to the layer 12 formed thereunder. Unfortunately, when following a conventional photolithography and etching process as described above, a pitting effect may be produced at the etch stop 11 between the active region and the peripheral region. This pitting can damage the etch stop 11, as illustrated in FIG. 3. The damaged etch stop layer may adversely impact the wafer during subsequent fabrication steps.